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參數(shù)資料
| 型號： | FAN7685 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | PC Power Supply Output Monitoring IC |
| 中文描述： | 電腦電源輸出監(jiān)控集成電路 |
| 文件頁數(shù)： | 11/14頁 |
| 文件大小： | 321K |
| 代理商： | FAN7685 |
FAN7685/FAN7686/FAN7687
11
state after a debounce of 38ms. The FPO pin can be connected to +5V(or up to +15V) through a pull-up resistor.
Under Voltage Protection
The FAN7685/FAN7686/FAN7687 provide undervoltage protection(UVP) for the +3.3V, +5V, and +12V power rails. When
an undervoltage condition appears at one of the VS33(+3.3V), VS5(+5V), or VS12(+12V) input pins for more than 73us, the
PGO goes low and FPO output goes high. Also, this fault condition will be latched until the PSON is toggled from low to high
or the Vcc falls below a minimum operating voltage.
When the power supply is turned on by the AC input or PSON, an internal UVP delay time is 75ms. But at normal state an
UVP delay time is only a 73us debounce time. The need for undervoltage protection is often overlooked in off-line switching
power supply system design. But it is very important in battery powered or hand-held equipment since the TTL or CMOS
logic often malfunctions under UVP condition.
Over Voltage Protection(OVP)
The overvoltage protection(OVP) of the FAN7685/FAN7686/FAN7687 monitor +3.3V, +5V, and +12V. When an overvoltage
condition appears at one of the +3.3V, +5V, or +12V input pins for more than 73us, the FPO output goes high and the PGO
goes low. Also, this fault condition will be latched until the PSON is toggled from low to high or Vcc drops below a minimum
operating voltage. During overvoltage condition, most power supplies have the potential to deliver higher output voltages than
those normally specified or required. In unprotected equipment, it is possible for output voltages to be high enough to cause
internal or external damage to the system. To protect the system under these abnormal conditions, it is common practice to pro-
vide overvoltage protection within the power supply.
Because TTL and CMOS circuits are very vulnerable to overvoltage, it is becoming industry standard to provide overvoltage
protection on all +3.3V, +5V, and +12V outputs. Therefore, not only the +3.3V and +5V rails for the logic circuits on the moth-
erboard need to be protected, but also the +12V peripheral devices such as the hard disk, flopply disk, and CD-ROM players
etc., need to be protected.
Over Current Protection
In bridge or forward type, off-line switching power supplies, usually designed from medium to large power, the overload pro-
tection design needs to be very precise. Most of these types of power supplies are sensing the output current for an overload
condition. The trigger point needs to be set higher than the maximum load in order to prevent false turn-on.
During safety testing the power supply might have tied the output voltage direct to ground. If this happens during the nomal
operating, this is called a short-circuit or over current condition. When it happens before the power supply turns on, this is
called a short-circuit power supply turn-on. It can happen during the design period, in the production line, at quality control
inspection or at the end user. The FAN7685/FAN7686/FAN7687 provide an UVP and OCP with a 75ms delay after PSON is
set low.
The FAN7685/FAN7686/FAN7687 provide overcurrent protection(OCP) for the 3.3V, 5V, and 12V rails. When an overcurrent
condition appears at the OCP comparator input pins for more than 73us, the FPO output goes high and PGO goes low. Also,
this fault condition will be latched until PSON is toggled from low to high or Vcc is removed.
The resistor connected between the RI pin and the GND pin will introduce an accurate I
O(RI)
for the OCP function. Of course,
a more accurate resistor tolerance will be better. The formula for choosing the RI resistor is V
RI
/I
O(RI)
. The I
O(RI)
range is
from 12.5uA to 62.5uA. Four OCP comparators and the I
O(RI)
section are supplied by VS12. Current drawn from the VS12pin
is less than 1mA.
Following is an example on calculating OCP for the 12V rail :
RI
V
I
O RI
)
--------------
20uA
--------------
60k
=
=
=
I
O RI
)
K
R
IS12
(
)
R
sense
(
)
=
×
×
I
OCP
(
Trip
–
)
×
I
OCP
(
Trip
–
)
20u
8
560
×
0.01
(
)
×
=
9.2A
=
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| FAN7685M | PC Power Supply Output Monitoring IC |
| FAN7685MX | PC Power Supply Output Monitoring IC |
| FAN7685N | PC Power Supply Output Monitoring IC |
| FAN7686 | ECONOLINE: REC3-S_DRW(Z)/H4,H6 - Safety standards and approval: EN 60950 certified, rated for 250VAV (LVD test report)- Applied for Ul 1950 Component Recognised Certification- 3W DIP Package- 4kVDC & 6kVDC Isolation- Regulated Output- Continuous Short Circiut Protection Auto-Restarting |
| FAN7686M | PC Power Supply Output Monitoring IC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN7685M | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PC Power Supply Output Monitoring IC |
| FAN7685MX | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PC Power Supply Output Monitoring IC |
| FAN7685N | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PC Power Supply Output Monitoring IC |
| FAN7686 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PC Power Supply Output Monitoring IC |
| FAN7686M | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PC Power Supply Output Monitoring IC |
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